I am keeping my Ritz because it essentially gives all the benefits of the CSR, at a cheaper cost, offers unlimited authorized users with Priority Pass, and a travel credit and free night which can easily offset the $450.00 fee.

You bring up an interesting point. I looked at the Marriott Boundless bonus terms and saw this:5 Free Night Award E-Certificates After You Spend $5,000 On Purchases In The First 3 Months From Account Opening: Eligibility for this product: The product is not available to either:

• current cardmembers of the Marriott Bonvoy® Premier credit card (also known as Marriott Rewards® Premier), Marriott Bonvoy Boundless® credit card (also known as Marriott Rewards® Premier Plus), Marriott Bonvoy Bold® credit card, or
• previous cardmembers of the Marriott Bonvoy® Premier credit card (also known as Marriott Rewards® Premier), Marriott Bonvoy Boundless® credit card (also known as Marriott Rewards® Premier Plus), or Marriott Bonvoy Bold® credit card, who received a new cardmember bonus within the last 24 months.

The Ritz card isn't even mentioned. It's possible Chase just forgot, since this card hasn't been available to new apps for almost 4 years. However, it seems like downgrading the Ritz to the Bold or Boundless would automatically disqualify you, but, since the Ritz isn't mentioned, your best bet may be to apply for a new Marriott Boundless, though I would also take screenshots of the terms and conditions, since you may have to fight after the fact...."Oh...we forgot to include the Ritz card...no bonus for you..."

My hope would be that Chase also includes Ritz holders for lounge access, if they are seriously looking to challenge Amex in a few years. I don't have any reason to open a new CSR, or CSP, at this time, but I'm not counting on it.